Method and apparatus for producing electrical contacts

ABSTRACT

A method and apparatus are provided for pressure-bonding a precious contact metal selected from the group consisting of silver, platinum, gold, palladium and alloys based on these metals to a metal substrate strip selected from the group consisting of copper, nickel, copper-base and nickel-base alloys to which the contact metal is cold bondable. The invention includes feeding a strip of the metal substrate towards a bonding station comprising upper and lower dies, one die being adapted to apply pressure to the other, producing a freshly cut or fractured surface in a portion of the strip before it reaches the bonding station, freshly cutting or fracturing the piece of precious contact metal, superposing the precious metal against the substrate with their freshly fractured surfaces in contact with each other, and then immediately applying impact pressure to the superposed metal portions by means of the pressure-applying die sufficient to deform the precious metal at least 30 percent of its thickness against the substrate whereby to cold bond the precious metal to the substrate. Precious metal cladded to a base metal of copper, nickel, copper-base and nickel-base alloys may be used as contact metal, the cladded precious metal being freshly fractured through the base metal side for bonding to the metal substrate strip.

United States Patent "21 Inventors Akira Shibata;

Shigeru Tabei, both of Tokyo, Japan [21 1 Appl. No, 788,258 [22] Filed Dec.3l, 1968 [45] Patented Aug. 24, 1971 l 7 3 I Assignee Chugai Electric industrial Co., Ltd.

Tokyo, Japan [32] Priority June 18, 1968 [33] Japan [3 l 43/422,070

[54] METHOD AND APPARATUS FOR PRODUCING ELECTRICAL CONTACTS 2 Claims, 17 Drawing Figs.

[52] [1.8. CI. 29/470.l, 29/47 1 .3 [5i] lut.Cl 1323!: 21/00 [50] Field of Search 29/470.1, 471.1, 471.3

[56] References Cited UNITED STATES PATENTS 3,151,385 10/1964 Gwyn,.lr. 29/470.1x 3,397,453 8/1968 Gwyn, Jr. 29/470.1 X 3,397,454 8/1968 Gwyn, Jr. 29/470.1 X 3,500,532 3/1970 Lozano et al. 29/470.1

Primary Examiner-John F. Campbell Assistant Examiner-Richard Bernard Lazerus Attorney-Hopgood and Calimafde ABSTRACT: A method and apparatus are provided for pressure-bonding a precious contact metal selected from the group consisting of silver, platinum, gold, palladium and alloys based on these metals to a metal substrate strip selected from the group consisting of copper, nickel, copper-base and nickel-base alloys to which the contact metal is cold bondable. The invention includes feeding a strip of the metal substrate towards a bonding station comprising upper and lower dies, one die being adapted to apply pressure to the other, producing a freshly cut or fractured surface in a portion of the strip before it reaches the bonding station, freshly cutting or fracturing the piece of precious contact metal, superposing the precious metal against the substrate with their freshly fractured surfaces in contact with each other, and then immediately applying impact pressure to the superposed metal portions by means of the pressure-applying die sufiicient to deform the precious metal at least 30 percent of its thickness against the substrate whereby to cold bond the precious metal to the substrate. Precious metal cladded to a base metal of copper, nickel, copper-base and nickel-base alloys may be used as contact metal, the cladded precious metal being freshly fractured through the base metal side for bonding to the metal substrate strip.

IPATENTED M1924 m SHEET 2 OF 4 FIGB m m R A mm m 9% Mm V 7 T v m A A0 I m PATENTEMusemn 3.60019 4 sum 3 OF 4 INVENTOR. Alf/RA 5/1/54 TA BY .S'fl/GIRU 7055/ PATENTEU M18248?! I 3,600,794

sum u [1F 4 INVENTOR. Alf/RA 5/1/84 TA BY 5/7/66? 79667 METHOD AND APPARATUS FOR PRODUCING ELECTRICAL CONTACTS The present invention relates to a method and apparatus for producing electrical contacts and, in particular, to a method and apparatus for pressure-bonding a piece of precious contact metal to a metal substrate to which the contact metal is cold-bondable.

It is known that electrical contacts can be produced by pressure bonding where both the contact metal and the metal substrate are mutually responsive to cold pressure bonding. In order to assure good bonding strength, it is important that the interface between the two metals be clean, otherwise the precious contact metal may tend to delaminate or strip away from the substrate metal during aggravated use in actual service. The term contact metal" employed herein has reference to an article of manufacture in which a piece or portion of a contact metal is bonded to a metal substrate which may be a flexible metal strip having good spring quality.

The contact metals to which this invention is directed include the ductile precious metals silver, platinum, gold and palladium and alloys based on these metals. The term metal substrate or strip, on the other hand, includes such metals as copper and copper alloys, such as brass, bronze, phosphor bronze, phosphor copper, etc., nickel and nickel alloys, such as nickel-copper alloys, nickel silver and the like.

It is the object of this invention to produce a contact element in which a strong joint or bonded interface is provided on the substrate.

Another object is to provide a method for producing an electrical contact element in which the contact metal is intimately and crystallographically bonded to the substrate.

A still further object is to provide an apparatus for carrying out the method aspects of the invention.

These and other objects will more clearly appear from the following disclosure and the appended drawings, wherein:

FIG. 1 is an exploded view showing one embodiment of a method for producing an electrical contact in accordance with the present invention;

FIG. 2 is a longitudinal cross section showing an electrical contact pressure-bonded according to the method of the present invention;

FIG. 3 is a view from the bottom showing the element employed in carrying out the method, while FIGS. 4 to 6 show in elevation the various aspects of the method from the cutting step to the bonding step;

FIGS. 7 and 8 are perspective views showing electrical contacts produced according to the method of the present inventron;

FIG. 9 shows in perspective a clad material having a thin film of precious material at one surface for use in producing a contact element;

FIGS. 10 and 11 are explanatory views showing a further embodiment of the method of the present invention, using the clad material shown in FIG. 9 as an electrical contact material;

FIG. 12 is a view in elevation showing a way of shearing the clad material, shown in FIG. 9, for use as an electrical contact material;

FIG. 13 is illustrative of one configuration of the clad material for use in producing electrical contact segments;

FIG. 14 is illustrative of one way of punching out segments .or pieces of clad material shown in FIG. 9;

FIGS. 15 and 16 are enlarged representations of the crystal configuration of a strip of substrate material; and

FIG. 17 is a view showing a structure of a sectioned surface of a precious metal.

According to one aspect of the invention, a method is provided for pressure-bonding a precious contact metal selected from the group consisting of silver, platinum, gold, palladium and alloys based on these metals to a metal substrate strip selected from the group consisting of copper, nickel, copperbase and nickel-base alloys to which the contact metal is coldbondable which comprises, feeding a strip of metal substrate towards a bonding station comprising upper and lower dies, one die being adapted to apply pressure to the other, producing a freshly cut or fractured surface in a portion of said strip before it reaches the bonding station, freshly cutting or fracturing the piece of precious contact metal, superposing the precious metal piece against the substrate with their freshly cut surfaces in contact with each other, and then immediately applying impact pressure to the superposed metal portions by means of the pressure-applying die sufficient to deform the precious metal at least 30 percent of its thickness against the substrate, whereby to bond the precious metal to the substrate. In producing the freshly cut surface on each of the metals, the metals may be sheared, shaved, pared, peeled, etc. One method is to partially shear the precious metal and fracture the remainder so as to produce a fresh coarse crystalline surface.

The apparatus employed for carrying out the method comprises a bonding station formed of upper and lower dies, with one die being adapted to apply pressure to the other, a pathway to the station along which the metal substrate strip is fed in supporting relationship with the lower die, means adjacent the pathway for cutting or fracturing a portion of the substrate surface to which the contact metal is to be bonded, and means associated with the pathway for cutting and feeding the contact metal is superposed relationship with the freshly cut or fractured surface of the substrate, whereby when the pressure-applying die is impacted against the superposed metals with their freshly cut surfaces in contact, a strong metallurgical bond is obtained by cold-pressure bonding.

Referring now to FIG. 1, one embodiment of the invention is shown in exploded view for producing an electrical contact in which a strip of substrate material 1, such as copper, brass, phosphor-bronze or nickel silver is fed along a pathway indicated by arrow 2 to a bonding station designated generally by S comprising a pair of dies 10 and 11 between which the strip is intermittently fed. The strip on the way to the bonding station passes by a shearing blade or knife edge 3 which is adapted to move into the direction of arrow 4 to cut, break away, shave or otherwise fracture a surface portion of the substrate to 'provide a fresh active surface 5. In indexing relationship with the intermittent feeding of the substrate strip, a wire or rod 6 of precious metal, e.g. of silver or silver-alloy, is fed in the direction of arrow 7 by a shear blade 8 which cuts a piece of the silver metal which is then delivered in the direction of arrow 9 and axially positioned as precious metal piece 13 between the dies 10 and 11, die 10 having a forming cavity 10' against which piece 13 of the precibus metal is molded when pressure is applied by the impact of one die relative to the other. In this case, die 10 is moved relative to support die 11, or both can move relative to the other, in the directing of arrow 12, the freshly fractured surface 5 being indexed centrally of lower die 11 which has an axially moveable pusher pin 14 within it. As die 10 contacts the die-supported strip, the end 15 of the pusher pin 14 hits the underface of strip 1 to form a cavity 15' therein (note FIG. 2) as die 10 deforms the freshly cut piece of silver 13 into molding cavity 10 which results in the electrical contact element of FIG. 2. Because both of the surfaces of the contact metal and the strip have been freshly cut or fractured, cold pressure bonding occurs at the interface leading to intimate crystallographic contact under pressure, which results in a strong metallurgical bond.

This embodiment of the invention will more clearly appear from FIGS. 3 to 5, FIG. 3 being a view looking from the bottom of the continuous operation. As will be observed, the strip of substrate metal 1 is intermittently fed along a pathway in the direction of arrow 2 so as to pass through guide 16 lying along the pathway having a cutter 3 slidably mounted at right angles to thelongitudinal axis of the strip. The strip then passes adjacent the surface of die 11 after a freshly cut or fractured surface 5 has been cut or sheared by cutter 3. In the meantime, a wire or rod 6 of precious metal is fed through guide 17. This is shown more clearly in FIG. 4 which is a vertical view of the apparatus of FIG. 3 as seen right side up.

. direction of arrow 4.

After the surface portion of strip 1 has been cut, it is moved under die 11 (FIG. 5). In the meantime, shear blade 8 shears off or fractures a piece of precious metal 6 which piece 13 is then delivered in bonding relation to the freshly cut surface of strip 1 in an axial position between the dies. The movement of piece 13 is synchronized with the intermittent movement of thestrip to the forming die. The header or die 10 with molding cavity 10' is then raised in the direction of arrow 12 (FIG. 6) and, at the same time, pusher pin 14 of die 11 is pushed downwardly in the direction of arrow 17. With this operation, the strip of substrate metal and the precious metal piece 13 disposed thereagainst are deformed and cold bonded with applied pressure atthe freshly fractured contact faces. The piece 13 of precious metal is deformed at least 30 percent of its original thickness intothe configuration of molding cavity 10, the precious metal assuming the configuration 13' shown in FIG. 6.

In the meantime, the broken face or fracture 5 of the substrate metal 1 is subjected to deformation on the reverse side thereof by pressure applied by pin 14, resulting in depression or cavity 15' shown in FIG. 2. By employing an automatically operable system so that the method is repeated sequentially along spaced positions on the substrate, a long strip 18 (FIG. 7) can be produced with the pieces of precious metal 13' pressure-bonded along the strip which thereafter is subjected to a series of punching or bending steps, for example in a machine press, to produce at high production rates electrical contact elements indicated by numeral 19 in FIG. 8.

To conserve on precious metals, cladded material 22 may be used as shown in FIG. 9 having a thin layer of precious metal 20 bonded, e.g. roll bonded,'on one surface of base metal 21 similar to the material of substrate metal 1. That is to say, the cladded material may have a base of a metal selected from-the group consisting of nickel, copper, nickel-base and copper-base alloys. The cladded material may be used as electrical contact material by cutting it on the base metal side and delivering it to the freshly cut or fractured substrate strip 1, the base metal part of the cladded material 22 being cold bonded to the freshly cut surface of strip 1, theexposed precious metal part being the contact metal portion. The cladded material 22 should be transferred in a direction parallel with.

the moving direction of the substrate strip 1 and be sheared by cutter 23 (FIG. 12) to provide freshly cut or fractured faces a and b on the base metal side, the piece being then superposed with the freshly cut base metal of the clad in contact with the freshly cut surface of strip 1 as shown in FIGS. 10 and 11, the left side of FIG. 1 1 being a similar view as FIG. 3.

The clad material 22 may be molded in an easily severable shape such as shown in FIG. 13; or, if desired, the clad material may be punched by means of a punch 24A to form a circular piece 25 as shown in FIG. 14, while the clad material is intermittently indexed in the direction of arrow 24. The circular piece 25 is inserted in a die 26 so that it projects slightly from its opposite end from the end surface of the die and then transferred for superposing on substrate strip 1 as it is cut or fractured at the projected end portion by cutter 27 moving in the direction of arrow 28 to form a freshly fractured surface. In this way, a cladded precious metal contact is pressure-bonded at spaced positions along substrate strip 1.

As stated hereinbefore, the method of pressure bonding is accomplished by freshly fracturing, or shaving, or skiving the surface of the substrate so as to expose unoxidized active metal surfaces. Since the substrate strip is normally manufactured by rolling, drawing, etc., the crystals at the surface are usually broken up into fine particles and elongated in the rolling direction as shown in the enlarged drawing of FIG. 15. Now, if the surface having such a crystal configuration is partly cut or broken away, such as by shaving, skiving, paring,

surface shearing, and the like, a coarse surface structure (FIG. 16) is produced which is characterized by high activity for pressure bonding. Alternatively, if a precious metal wire or rod is partially cut or sheared at one portion, such as 29 in FIG. 17, and then fractured so as to providea fractured surface 30 constituting about 90 percent of the whole area, the fractured surface is generally coarse and has high activity for pressure bonding. Thus, by contacting both coarse fractures together and applying high impact pressure to the superposed metals so that the precious metal piece is deformed at least about 30 percent of its original thickness, a strong crystallographic bond is formed by virtue of the fact that the coarse active metal surfaces at the interface under high pressure are metallurgically merged with each other. This method enables the economical production of electrical contact elements at a very high rate or production.

As stated herein, the method of the invention is applicable to contact metals selected from the group consisting of silver, platinum, gold, palladium and alloys based on these metals. Examples of such alloys are: 10 percent Cd and the balance Ag; 90 percent Ag-lO percent CdO; 90 percent Ag- 1 0 percent Ni; 70 percent Ag-30 percent Pd; 74.5 percent Ag-25 percent Au-0.5 percent Ni; 95 percent Ag-S percent Ni; 90 percent Ag-lO percent Cu; 72 percent Ag-26 percent Cu-2 percent Ni; 97 percent Ag-3 percent Pd; 97 percent Ag-3 percent Pt; 95 percent Pt-S percent Ir; percent Pt-lS percent ir; percent Pt-IO percent Ru; 96 percent Pt-4 percent W; 90 percent Pd-IO percent Ru; 70 percent Pd3 percent Ag; 72 percent Pd-26 percent Ag-2 percent Ni; 45 percent Pd-30 percent Ag- 20 percent Au-5 percent Pt; 90 percent Au-lO percent Cu; 75 percent Au-25 percent Ag; 69 percent Au-25 percent Ag-6 percent Pt; 41.7 percent Au-32.5 percent Cu- 1 8.8 percent Ni- 7 percent Zn; and like electrical contact alloys. The foregoing compositions are merely illustrative of electrical contact metals based substantially on the precious metals Ag, Pt, Au and Pd.

As stated with respect to the substrate metals, these may include nickel, copper, nickel-base and copper-base alloys, such as nickel silver, nickel-copper alloys (e.g. 60 percent Ni-40 percent Cu); alloys of copper-zinc, beryllium-copper, copperphosphorous, and the like.

Nickel silver, otherwise known as German silver, may comprise 45 to 65 percent copper, 15 to 40 percent zinc and 8 to 35 percent nickel. A typical example of nickel silver is one containing 55 percent copper, 25 percent zinc and 20 percent nickel. The following alloys are available in sheet or strip form: 54 percent copper, 16 percent zinc .and 30 percent nickel; 58 percent copper, 24 percent zinc and 18 percent nickel; and 60 percent copper, 30 percent zinc and 10 percent nickel.

Typical copper-zinc alloys include those falling in the range of 5 to 40 percent zinc and the balance copper. The berylliumcopper alloys include those containing about 1 percent to to 3 percent of beryllium and the balance substantially copper, while the coppenphosphorous alloys may contain about 0.02 percent phosphorous and the balance substantially copper, said alloys also containing up to 10 percent tin.

The same substrate metals may be used as the base metal for cladded precious metals in order to save on the use of precious metals.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and the appended claims.

We claim:

1. A method of pressure-bonding a precious contact metal selected from a group consisting of silver, platinum, gold, palladium and alloys based on these metals to a metal substrate strip selected from the group consisting of copper, nickel,

copper-base and nickel-base alloys to which the contact metal is cold bondable which comprises,

providing a pathway having a bonding station located therealong comprising upper and lower dies disposed above and below said pathway, respectively, one die being adapted to apply pressure to the other, said pathway having located adjacent and transverse thereto and before said bonding station first cutting means moveable transverse to said pathway for producing a freshly fractured surface on a metal substrate strip moved along said pathway and second cutting means located transverse of said bonding station for cutting pieces of a precious metal element fed thereto and for transporting each of said pieces to said bonding station, intermittently feeding said substrate strip along said pathway towards said bonding station, actuating said first cutting means transverse to the surface of said strip whereby to produce a fresh fracture at a selected surface portion thereof, moving said strip to said bonding station,

feeding a precious metal element to said second cutting means and freshly cutting a piece of said element and transporting said piece to said bonding station in superposed relationship with the freshly cut strip at said station,

and then immediately applying impact pressure to the superposed metals by means of the pressure-applying die sufficient to deform the precious metal at least 30 percent of its thickness against the substrate whereby to cold bond said precious metal to the substrate.

2. The method of claim 1, wherein the precious metal is provided with a cladded layer on a base metal selected from the group consisting of copper, nickel, copper-base and nickelbase alloys, wherein the cladded piece of metal is freshly fractured at the base metal side, and wherein the fractured side of the cladded piece of metal is superposed on the freshly fractured part of the substrate strip before the two are cold pressure-bonded to each other. 

2. The method of claim 1, wherein the precious metal is provided with a cladded layer on a base metal selected from the group consisting of copper, nickel, copper-base and nickel-base alloys, wherein the cladded piece of metal is freshly fractured at the base metal side, and wherein the fractured side of the cladded piece of metal is superposed on the freshly fractured part of the substrate strip before the two are cold pressure-bonded to each other. 